TIAGABINE HYDROCHLORIDE

TIAGABINE HYDROCHLORIDE (ti-a'ga-been) Gabitril Filmtabs Classifications: anticonvulsant; gaba inhibitor; Therapeutic: anticonvulsant Prototype: Valproic acid sodium (sodium valproate) Pregnancy Category: C

Availability

2 mg, 4 mg, 12 mg, 16 mg, 20 mg tablets

Action

GABA inhibitor for the treatment of partial epilepsy. Potent and selective inhibitor of GABA uptake into presynaptic neurons; allows more GABA to bind to the surfaces of postsynaptic neurons in the CNS.

Therapeutic Effect

Effectiveness indicated by reduction in seizure activity.

Uses

Adjunctive therapy for partial seizures.

Contraindications

Hypersensitivity to tiagabine; pregnancy (category C); lactation; children <12 y.

Cautious Use

Liver function impairment; history of spike and wave discharge on EEG; status epilepticus.

Route & Dosage

Seizures Adult: PO Start with 4 mg q.d., may increase dose by 4–8 mg/d qwk (max: 56 mg/d in 2–4 divided doses) Adolescent (12–18 y): PO Start with 4 mg q.d., after 2 wk may increase dose by 4–8 mg/d qwk (max: 32 mg/d in 2–4 divided doses)

Administration

Oral

• Give with food.
• Make dosage increases, when needed, at weekly intervals.
• Store at 15°–30° C (59°–86° F) in a tightly closed container and protect from light.

Adverse Effects (≥1%)

Body as a Whole: Infection, flu-like syndrome, pain, myasthenia, allergic reactions, chills, malaise, arthralgia. CNS: Dizziness, asthenia, tremor, somnolence, nervousness, difficulty concentrating, ataxia, depression, insomnia, abnormal gait, hostility, confusion, speech disorder, difficulty with memory, paresthesias, emotional lability, agitation, dysarthria, euphoria, hallucinations, hyperkinesia, hypertonia, hypotonia, myoclonus, twitching, vertigo. Risk of new-onset seizures. CV: Vasodilation, hypertension, palpitations, tachycardia, syncope, edema, peripheral edema. GI: Abdominal pain, diarrhea, nausea, vomiting, increased appetite, mouth ulcers. Respiratory: Pharyngitis, cough, bronchitis, dyspnea, epistaxis, pneumonia. Skin: Rash, pruritus, alopecia, dry skin, sweating, ecchymoses. Special Senses: Amblyopia, nystagmus, tinnitus. Urogenital: Dysmenorrhea, dysuria, metrorrhagia, incontinence, vaginitis, UTI.

Interactions

Drug: Carbamazepine, phenytoin, phenobarbital decrease levels of tiagabine. Use with antidepressants, antipsychotics, stimulants, and narcotics may increase seizure risk. Herbal: Ginkgo may decrease anticonvulsant effectiveness. Evening primrose oil may affect seizure threshold.

Pharmacokinetics

Absorption: Rapidly absorbed; 90% bioavailability. Peak: 45 min. Distribution: 96% protein bound. Metabolism: In liver, probably by cytochrome P450 3A isoform. Elimination: 25% in urine, 63% in feces. Half-Life: 7–9 h (4–7 h with other enzyme-inducing drugs).

Nursing Implications

Assessment & Drug Effects

• Lab tests: Measure plasma levels of tiagabine before and after changes are made in the drug regimen.
• Be aware that concurrent use of other anticonvulsants may decrease effectiveness of tiagabine or increase the potential for adverse effects.
• Monitor carefully for S&S of CNS depression.

Patient & Family Education

• Do not stop taking drug abruptly; may cause sudden onset of seizures.
• Exercise caution while engaging in potentially hazardous activities because drug may cause dizziness.
• Use caution when taking other prescription or OTC drugs that can cause drowsiness.
• Report any of the following to the physician: Rash or hives; red, peeling skin; dizziness; drowsiness; depression; GI distress; nervousness or tremors; difficulty concentrating or talking.

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Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug